The invention relates to the general field of integrated circuit manufacture with particular reference to chemical mechanical polishing (CMP) and surface finishes obtained therewith.
As the number of layers in an integrated circuit has grown, so has the need for frequent planarizing steps. Most purely chemical methods for etching tend to follow the contours of the surface being etched and/claim or to selectively etch parts of heterogeneous surfaces. Purely mechanical methods for surface removal (i.e. polishing) tend to provide a planar etch front but, if all surface damage is to be eliminated, require slurries so fine as to reduce etch time to unacceptably low levels.
The CMP process represents an excellent compromise between the two approaches. It has been applied for STI (shallow trench isolation), pre-metal dielectric, inter metal dielectric (IMD), to cite a few examples. The more advanced the technology is, the more likely it is that CMP processes will be used. One disadvantage of CMP processes, however, is that complete elimination of all scratches is hard to achieve. This is illustrated schematically in FIGS. 1 and 2 which show a substrate 11 on which are two protuberances 12 (typically metal lines) which have been over-coated with a layer 13 (typically a dielectric) resulting in an uneven top surface 14. After CMP, surface 14 is now essentially planar except for the presence of micro-scratches 24. By xe2x80x9cmicro-scratchesxe2x80x9d we imply that the scratches are no more than about 5,000 Angstroms deep.
From the FA (failure analysis) of products, the killing ratio for micro-scratches associated with CMP and other processes has been determined to be as much as 2 to 3% per layer. There is therefore strong motivation to eliminate this problem. Several methods had been tried to reduce such micro-scratches. For example, the slurry (abrasives), pad life, rotation speed, downward pressure (between wafer and pad), and oxide buffing have all been tried with varying degrees of success, with oxide buffing doing best. However, this latter approach turns out to be at the expense of range and uniformity.
The present invention discloses an approach that places no constraints on, and requires no changes to, the CMP process itself. Nor does it cause any reduction in range or uniformity. As will be seen, it can be applied in-situ or ex-situ, depending on the overall particular processing situation.
A routine search of the prior art was performed with the following references of interest being found:
U.S. Pat. No. 6,180,525(Morgan) shows a CMP process involving scratches. U.S. Pat. No. 5,915,175 (Wise) reveals a process to reduce CMP induced damage. U.S. Pat. No. 6,110,795 (Liao) and U.S. Pat. No. 5,516,729 (Dawson et al.) show CMP/scratch related processes.
It has been an object of at least one embodiment of the present invention to provide a process whereby micro-scratches caused by cMP, or similar processing steps, may be removed.
Another object of at least one embodiment of the present invention has been that said process require little or no modification to the CMP, or similar, process itself.
Still another object of at least one embodiment of the present invention has been that said process be executable in in-situ or ex-situ modes.
These objects have been achieved by exposing the surface under treatment to a gas plasma after CMP (or other process that could produce micro-scratches) has been completed. Additionally, the invention discloses that the small amount of material that gets removed through exposure to the plasma may be replaced by deposition either in-situ or ex-situ. The added material may be the same as the removed material or a different material.